U.S. Pat. Nos. 4,545,644 and 4,691,986, which are hereby incorporated by reference, describe optical connectors in which optical fibers are cemented into a pair of glass ferrules that are subsequently mated in a secondary alignment sleeve. U.S. Pat. No. 4,545,644 discloses an optical interconnection which is tuned using a secondary alignment sleeve. The '986 patent discloses a method of forming an optical connector using a "continuous" ferrule material in order to form a connection in which the receiving bores are inherently in nearly perfect alignment. The product based on these patents is now sold under the trade name of the ATT Rotary Mechanical Splice.
This same interconnect technology has also been used to build a unique wavelength selective coupler as disclosed in U.S. Pat. No. 4,701,011. This patent teaches how to embed a short piece of multimode graded index fiber in the end of a glass ferrule so that a small, 1/4 pitch, graded index rod lens is formed. When a single mode fiber is coupled to this lens, the light emerging from the single mode fiber will be collimated. Using this technique, a wavelength selective signal mode fiber optic coupler can be constructed by placing a wavelength selective filter between two ferrules housing single mode fibers.
Other coupler designs which employ beamsplitting techniques are also well known in the optical communications industry. For example, U.S. Pat. No. 4,306,765 shows a fiber optic coupler using a dielectric beamsplitter deposited on a polished fiber face.
A major limitation of most prior art optical couplers is that these couplers do not incorporate a low cost, low loss mechanism for easily connecting the coupler to a fiber optic network. For example, while the optical coupler disclosed by Winzer et al. in U.S. Pat. No. 4,306,765 provides a low loss optical coupler, it is produced with fiber optic "pigtails" which must be either spliced or otherwise processed in order to connect the coupler to a fiber network. In another example, while the coupler structure proposed by Emkey et al. in U.S. Pat. No. 4,701,011 utilizes elements that interconnect, the coupler disclosed does not include apparatus for integrating the device into a optical fiber system; rather the disclosed device has pigtails that must be connected to a fiber optic system in an undisclosed manner.
It is therefore an object of the present invention to provide an optical fiber coupling structure which can achieve excellent coupling efficiency and which also incorporates an interconnection port for connecting the coupling structure to an additional optical channel.